From time to time, Service Packs are released with all the latest updates and bug fixes included. If you have the original release or an older service pack installed, there is no need to re-install or upgrade! All you need to do is visit the Software Updates page in webconfig to install all the available updates.
ClearOS Enterprise 5.1 Service Pack 1 was released March 5, 2010.
The full release notes for ClearOS Enterprise 5.1 can be found here.